This invention relates to a method of manufacturing rings for reinforcing the beads of tires of the type without a separate inner tube, known also as "tubeless tires", to the use of a special wire for carrying out this method, and to rings produced by the method.
In tires, the rubber base present between the heel and the toe of the two beads has the external apperance of a frustoconical zone. Upon the mounting of the tire on a rim, the base of each bead is seated on a zone of the rim which is of suitable conicity, this zone being termed the bead seat. The base not only plays an essential role in holding the bead, that is to say the tire, firmly on the rim but, together with the bead seat, it forms the sealing joint between the tubeless tire and the rim. For this purpose, the bead seats of tires have a conicity of between about 5.degree. and about 15.degree..
The tire bead rings assure the nonstretching of the bead and serve as anchoring for the carcass reinforcement. In tubeless tires there are preferably employed rings of the package type produced by winding steel wires in adjoining turns on a form of revolution consisting of the groove of a pulley. One can thus impart to the radial cross section of the ring an axial width greater than its radial height and a radially inner frustoconical face which may or may not be parallel to the bead seat. In order to stabilize the shape of the radial cross section of the ring against defects in the shaping and molding of the tire, steel wires of circular cross section have been replaced by steel wires of rectangular cross section (French Patent No. 73 08228 corresponding to U.S. Pat. No. 3,949,800). In order to obtain a radial cross section of the ring, the radially inner face of which is linear, it has been proposed to impart to the wires of rectangular cross section, prior to their winding, a permanent curvature which is directed towards the inside of the tire (German Provisional Patent No. 26 53 553).
Whatever the cross section of the steel wire used, the radial cross sections of these rings do not remain unchanged under the effect of the manufacturing forces and the stresses in use caused by the carcass reinforcement which is anchored around the rings.
These defects seem to come from the elasticity, that is to say the residual stresses stored in the steel wires during the winding of them on the form of revolution. The coherence of the elements forming the ring, seen in radial cross section, is no longer assured. The wires have a tendency to reorient the principal axis of inertia of their radial cross section, corresponding to the highest principal moment of inertia, parallel to the axis of winding of the wires. The wires then have a tendency to resume the shape which they had prior to their winding. This results not only in a disorganization of the initial structure imparted to the ring but also in empty spaces between the wires forming the ring.